The present invention relates generally to methods of making nonwoven fabrics, and more particularly to a method of manufacturing at a high rate of speed a nonwoven fabric exhibiting improved physical characteristics while retaining image, permitting use of the fabric in a wide variety of consumer applications.
The production of conventional textile fabrics is known to be a complex, multi-step process. The production of fabrics from staple fibers begins with the carding process where the fibers are opened and aligned into a feed stock known as sliver. Several strands of sliver are then drawn multiple times on a drawing frames to further align the fibers, blend, improve uniformity as well as reduce the sliver""s diameter. The drawn sliver is then fed into a roving frame to produce roving by further reducing its diameter as well as imparting a slight false twist. The roving is then fed into the spinning frame where it is spun into yarn. The yarns are next placed onto a winder where they are transferred into larger packages. The yarn is then ready to be used to create a fabric.
For a woven fabric, the yarns are designated for specific use as warp or fill yarns. The fill yarns (which run on the y-axis and are known as picks) are taken straight to the loom for weaving. The warp yarns (which run on the x-axis and are known as ends) must be further processed. The large packages of yarns are placed onto a warper frame and are wound onto a section beam were they are aligned parallel to each other. The section beam is then fed into a slasher where a size is applied to the yarns to make them stiffer and more abrasion resistant, which is required to withstand the weaving process. The yarns are wound onto a loom beam as they exit the slasher, which is then mounted onto the back of the loom. The warp yarns are threaded through the needles of the loom, which raises and lowers the individual yarns as the filling yarns are interested perpendicular in an interlacing pattern thus weaving the yarns into a fabric. Once the fabric has been woven, it is necessary for it to go through a scouring process to remove the size from the warp yarns before it can be dyed or finished. Currently, commercial high speed looms operate at a speed of 1000 to 1500 picks per minute, where a pick is the insertion of the filling yarn across the entire width of the fabric. Sheeting and bedding fabrics are typically counts of 80xc3x9780 to 200xc3x97200, being the ends per inch and picks per inch, respectively. The speed of weaving is determined by how quickly the filling yarns are interlaced into the warp yarns, therefore looms creating bedding fabrics are generally capable of production speeds of 5 inches to 18.75 inches per minute.
In contrast, the production of nonwoven fabrics from staple fibers is known to be more efficient than traditional textile processes as the fabrics are produced directly from the carding process.
Nonwoven fabrics are suitable for use in a wide variety of applications where the efficiency with which the fabrics can be manufactured provides a significant economic advantage for these fabrics versus traditional textiles. However, nonwoven fabrics have commonly been disadvantaged when fabric properties are compared, particularly in terms of surface abrasion, pilling and durability in multiple-use applications. Hydroentangled fabrics have been developed with improved properties which are a result of the entanglement of the fibers or filaments in the fabric providing improved fabric integrity. Subsequent to entanglement, fabric durability can be further enhanced by the application of binder compositions and/or by thermal stabilization of the entangled fibrous matrix.
U.S. Pat. No. 3,485,706, to Evans, hereby incorporated by reference, discloses processes for effecting hydroentanglement of nonwoven fabrics. More recently, hydroentanglement techniques have been developed which impart images or patterns to the entangled fabric by effecting hydroentanglement on three-dimensional image transfer devices. Such three-dimensional image transfer devices are disclosed in U.S. Pat. No. 5,098,764, hereby incorporated by reference, with the use of such image transfer devices being desirable for providing a fabric with enhanced physical properties as well as an aesthetically pleasing appearance.
For specific applications, a nonwoven fabric must exhibit a combination of specific physical characteristics. For example, fabrics used in the home should be soft and drapeable, yet withstand home laundering, and be resistant to abrasion (which can result in fabric pilling). Fabrics used in the home must also exhibit sufficient strength and tear resistance, and colorfastness. These are among the characteristics which have been identified as being desirable for so-called xe2x80x9ctop-of-the-bedxe2x80x9d applications, such as comforters, pillows, dust ruffles, and the like.
Heretofore, attempts have been made to develop nonwoven fabrics exhibiting the necessary aesthetic and physical properties. U.S. Pat. No. 3,933,304, discloses a washable spunlaced nonwoven cloth, with this patent contemplating use of a PAE binder composition (polyamide-amine-epichorohydrin) with inclusion of cotton fiber in the fibrous matrix.
U.S. Pat. No. 3,988,343, discloses a nylon fabric treated with a mixture of acrylic polymer and latex binder with tinting pigments. U.S. Pat. No. 5,874,159 contemplates providing a spunlaced fabric structure with durability by the provision of a bonding material in the form of a thermal plastic polymer, which may be provided in the form of a net, an apertured or punctured film, or molten drop form. The bonding material acts to join layers or laminations from which the fabric is formed.
Notwithstanding various attempts in the prior art to develop a nonwoven fabric acceptable for home use applications, a need continues to exist for a nonwoven fabric which provides the desired softness and drapeability, as well as the requisite mechanical characteristics.
The present invention is directed to a method of forming a nonwoven fabric, which exhibits enhanced physical characteristics which are achieved through enhanced imaging and patterning on a three-dimensional image transfer device. In particular, the present invention contemplates that a fabric is formed from a precursor web which is subjected to hydroentanglement on a moveable imaging surface of the three-dimensional image transfer device. Enhanced imaging is achieved, with resultant improvement in physical properties, by advancing the precursor web onto the imaging surface at a rate substantially equal to the rate at which the imaging surface moves. By formation in this fashion, hydroentanglement of the precursor web results in improved entanglement of the fibrous matrix from which the web is formed, comprising either staple length fibers and/or filaments. Enhancement of Z-direction entanglement has been observed, with resultant fabrics exhibiting characteristics which, in many important respects, are like those of traditional woven fabrics.
In accordance with the present invention, a method of making a nonwoven fabric embodying the present invention includes the steps of providing a precursor web comprising a fibrous matrix. While use of staple length fibers is typical, the fibrous matrix may comprise substantially continuous filaments. In a particularly preferred form, the fibrous matrix is carded and cross-lapped to form a precursor web. It is also preferred that the precursor web be subjected to pre-entangling on a foraminous forming surface prior to imaging and patterning.
The present method further contemplates the provision of a three-dimensional image transfer device having a movable imaging surface. In a typical configuration, the image transfer device may comprise a drum-like apparatus which is rotatable with respect to one or more hydroentangling manifolds.
The precursor web is advanced onto the imaging surface of the image transfer device so that the web moves together with the imaging surface. Hydroentanglement of the precursor web is effected to form an imaged and patterned fabric. Significantly, the rate at which the precursor web is advanced onto the moveable imaging surface is substantially equal to the rate of movement of the imaging surface. Advancement of the precursor web in this fashion acts to minimize tension therein, with support of the precursor web being contemplated in order to minimize tension.
As will be appreciated, minimization of tension in the precursor web acts to desirably enhance imaging and patterning of the precursor web on the image transfer device. Enhanced fiber entanglement is achieved, with resultant improvement in physical properties of the fabric being formed. Z-direction entanglement is particularly improved.
Subsequent to hydroentanglement, the imaged and patterned fabric may be subjected to one or more variety of post-entanglement treatments. Such treatments may include application of a polymeric binder composition, mechanical compacting, application of a flame-retardant composition, and like processes.
A further aspect of the present invention is directed to a method of forming a durable nonwoven fabric which exhibits a sufficient degree of softness and drapeability, while providing the necessary resistance to tearing and abrasion, to facilitate use in a wide variety of applications. The fabric exhibits a high degree of launderability, thus permitting its use in those applications in which the fabric may become soiled, and thus require home laundering.
A method of making the present durable nonwoven fabric comprises the steps of providing a precursor web which is subjected to hydroentangling. A polyester/nylon fiber blend has been found to desirably yield soft hand and good fabric drapeability. The precursor web is formed into an imaged and patterned nonwoven fabric by hydroentanglement on a three-dimensional image transfer device. The image transfer device defines three-dimensional elements against which the precursor web is forced during hydroentangling, whereby the fibrous constituents of the web are imaged and patterned by movement into regions between the three-dimensional elements of the transfer device.
In the preferred form, the precursor web is hydroentangled on a foraminous surface prior to hydroentangling on the image transfer device. This pre-entangling of the precursor web acts to integrate the fibrous components of the web, but does not impart imaging and patterning as can be achieved through the use of the three-dimensional image transfer device.
Subsequent to hydroentangling, the imaged and patterned nonwoven fabric is treated with a polymer binder composition to lend further integrity to the fabric structure. The polymeric binder composition is selected to enhance durability characteristics of the fabric, while maintaining the desired softness and drapeability of the patterned and imaged fabric.
In order to enhance softness and drapeability of the present nonwoven fabric after it has been treated with the binder composition, the fabric may be subjected to slight mechanical compaction, such as by sanforizing (Sanforized(copyright) is a registered trademark of Cluett, Peabody and Co., Inc). Such treatment has been found to enhance hand and drapeability of the fabric, without undesirably adversely affecting the mechanical characteristics of the fabric.
Other features and advantages of the present invention will become readily apparent from the following detailed description, the accompanying drawings, and the appended claims.